Payable

A function cannot receive Ether, unless marked as payable .

• address payable myAddress

• function myFunction() public payable{}

• If a function/address is not marked as payable and receives Eth - it will fail.

// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.1;

contract SendMoneyExample {
    uint public balanceReceived;      

    function receiveMoney() public payable {
        balancedReceived += msg.value;          //msg: global always-existing object
    }

    function getBalance() public view returns(uint) {
        return address(this).balance
    }
}

uint public balanceReceived

• public state variable -> getter function auto-created. So we can always query its value.

• therefore, we don't need getBalance -> this is just an example.

balanceReceived += msg.value

• The msg-object is a global always-existing object containing a some information about the ongoing transaction.

msg object fields

• The two most important properties are .value and .sender.

  • .value contains the amount of Wei that was sent to the smart contract.

  • .sender contains the address that called the Smart Contract.

address(this).balance

• A variable of the type address always has a property called .balance which gives you the amount of ether stored on that address.

• It doesn't mean you can access them, it just tells you how much is stored there. Remember, it's all public information.

• address(this) converts the Smart Contract instance to an address. So, this line essentially returns the amount of Ether that are stored on the Smart Contract itself.